The present invention relates to a drafting material comprising a plastic support having on at least one surface an adhesive layer, a layer of pigmented or clear lacquer and an antistatic top layer which contains a homo- or copolymer of vinyl acetate.
Drafting materials, such as, for example, drafting films, are generally made from a plastic support of cellulose acetate, polyvinyl chloride, polypropylene, or preferably polyester, particularly polyethylene terephthalate which has an adhesive layer on at least one surface. The film is preferably coated with a pigmented lacquer system, in order to obtain a surface which can be marked or written on with pencil lead and ink. The material can also be equipped with a separate top layer which is applied to the layer of pigmented lacquer, in order to facilitate ink adherence. In those cases where the film is to be written on with ink only, a transparent lacquer or an antistatic top layer can be applied directly to the adhesive layer.
There is known a film material which can be marked (German Offenlegungsschrift No. 2417879, equivalent to British Pat. No. 1,448,889) and which comprises a top layer, which is applied to a layer of pigmented lacquer and which consists of a homopolymer of vinyl acetate, a polymeric compound which mainly contains hydroxyl-containing or carboxyl-containing monomers, and a hydrophobicity-imparting agent. A top layer of this type is sensitive to water or moisture. If the hydrophobicity-imparting agent content is high, the wetting with aqueous drawing ink is also unsatisfactory. Finally, this film material lacks an antistatic finish.
Furthermore, a top layer has been disclosed for a matte film material which can be marked (German Offenlegungsschrift No. 2347324, equivalent to U.S. Pat. No. 3,857,729) and which includes a polyester support, a layer of film-forming cellulose lacquer thereon and an external layer as an antistatic coating. The antistatic agents used are water-soluble, relatively complex compounds of sulfonated polystyrene and a cycloaliphatic amine salt of an alcohol sulfate. Such a layer has the disadvantage that it is sensitive to humidity, and can always be dissolved from the surface with water.
A further disclosure (German Offenlegungsschrift No. 2513422, equivalent to British Pat. No. 1,497,657) describes a coated plastic film, such as a polyester film, having, if appropriate, applied to a substrate layer of acrylic or methacrylic acid copolymer, a layer which consists of an unhydrolyzed or partially hydrolyzed polymer or copolymer of vinyl acetate and a resinous component which is suitable for intramolecular crosslinking. The vinyl acetate copolymer contains at least 50 mole percent of vinyl acetate, and can contain a very wide variety of compounds as comonomers, such a dialkyl maleate, 2-ethylhexyl acrylate, ethylene, vinyl chloride or a vinyl ester of Versatic acid. Such a coated film is said to also be suitable for preparing drawing films provided appropriate additives are incorporated therein. However, no information is provided about a relevant composition. It is true that the incorporation of finely divided delustrants is likely to modify the film material in such a way that it can be marked, to a certain extent, with pencil leads, but additives of a kind suitable for writing with ink require considerable experimental effort with respect to the compatibility and adjustment of the substances relative to one another and required properties, such as the ability of inks to wet the surface in a suitable way, adhesion to the surface and correctability of symbols, and the like. This applies in particular to a possible addition of antistatic agents, which, as is known from experience, impairs ink-writing properties, on occasion to such an extent that the inks no longer wet.
In German Pat. No. 32,07,122, a drafting film is described which contains a pigmented lacquer system comprising an acrylic or methacrylic acid ester copolymer which includes at least 50% by weight of an ester monomer, the alcohol component of which has a chain length of at least four carbon atoms, and to which an antistatic agent selected from among the salts of polymeric sulfonic acids is added. This drafting film can be suitably marked with inks, although the edges of the ink lines are not yet sharp enough, and its antistatic finish, particularly if applied as top layer, is not sufficiently resistant to the action of water.